In oilfield applications, there are many instances where it is desirable to know the viscosity or rheological properties of a fluid. For example, a fracturing operation involves pumping a fracturing fluid into a subterranean zone in order to create fractures in the rock of the subterranean zone. The fractures provide flow passages that convey fluids between the subterranean zone and the wellbore. The distance that the fractures penetrate into the subterranean zone (i.e., fracture length) is a function of, among other things, the pressure that can be generated within or near the subterranean zone. Furthermore, this fracture length is a also a function of flow rate into the subterranean zone. To optimize pressure and flow rate at the subterranean zone, the fracturing fluid is typically injected rapidly into or near the subterranean zone. Rapid injection has large associated costs, though, such as the amount of pumping power required to quickly inject the fracturing fluid. The pumping power may be reduced and the fracturing fluid may be introduced more quickly by altering (e.g., lowering) the frictional drag characteristics of the fluid, such as with friction reducing additives. The amount of some friction reducing additives must be carefully controlled to maintain the friction reduction of the fracturing fluid at a desired level. The width of the created fracture is function of the fluid viscosity of the fracturing fluid at the subterranean zone. Gelling agents used to generate viscosity have costs and other undesirable effects. The fluid viscosity must be carefully controlled to maintain the viscosity at a desired level to optimize desired effects (e.g., fracture width) while minimizing undesired effects (e.g., cost).